The invention relates to a self-balancing vehicle with at least three wheels resting on the ground, at least two of which wheels are arranged on either side of the center of gravity with respect to the longitudinal axis of the vehicle, and at least one of which wheels is directionally controllable, and wherein at least one section of the vehicle is tiltable about the longitudinal axis of the vehicle for the purpose of producing and/or maintaining a change in direction of the directionally controllable wheel during travel, a control element for controlling the at least one directionally controllable wheel, and a power-assisted tilt element for tilting said vehicle section about the longitudinal axis of the vehicle.
A four-wheeled motor vehicle having a rear part which can tilt around a longitudinal axis with respect to a front part is described in EP-A-0592377. To this end a mechanical transmission links the axis of the front steering unit, which may be handle bars, to a tilt unit. A servo-mechanism of the hydraulic type may be controlled by the front steering unit. Two servo-control actuators are operated in opposite directions by a servo distributor subordinate to the front steering unit to provide the inclination of the chassis in both directions. The known vehicle has as a disadvantage that at a given angular position of the steering unit, a fixed inclination is imparted. No accommodation for drivers of varying weight is possible. Furthermore, driving speeds are not taken into account. Turning the steering units in a stationary position will cause the same inclination as turning the steering unit while driving at relatively high speed.
The aim of the invention is to provide a control system with which the tilting of the vehicle or a section of the vehicle towards the inside of the bend can be achieved efficiently, such that good stability can be ensured under all driving conditions, in particular at speeds higher than those which are customary when driving the vehicle into or out of a parking space.
To this end, the vehicle according to the invention is characterized in that the vehicle is self-balancing and comprises a sensor connected to the directionally controllable wheel for registering the magnitude and the direction of the load which is to be applied to the directionally controllable wheel for the purpose of producing and/or maintaining a change in direction thereof during travel, the sensor being connected to the tilt element to produce a tilt as a function of the registration by the sensor.
The steering force/the steering torque is measured, as it has been found that these load parameters give the best results. A force/torque of this type is generated automatically when the directionally controllable wheel has a certain castor, whilst the angle of tilt does not correspond to the driving speed and the bend radius intended by turning the steering wheel. By making use of this knowledge, the degree of tilt can be controlled by measurement of the said force/torque. In comparison with, for example, the known use of acceleration sensors, particularly natural direct driving characteristics are obtained by means of the present invention, so that the vehicle can also be operated by inexperienced persons.
From EP-A-153521 a vehicle body tilting system is known in which a hydraulic ram is connected to a spool type control valve. The control valve is actuated by the steering mechanism to quickly initiate a tilting movement upon turning of the steering mechanism. The control valve is also connected to a pendulum which progresses the tilting movement until the normally upright axis of the vehicle body is in line with the resultant vector of gravity and the centripetal acceleration.
A tilting system of this kind is relatively complex, has a certain lag and may be liable to malfunctioning in case the swinging motion of the pendulum is obstructed.
The use of a simultaneously tiltable directionally controllable wheel is to be preferred, by which means a particularly simple control system can be used. With this system it is fairly easy to achieve equilibrium for every tilt position since in every position of equilibrium for the tilt movement the steering load will then be zero or virtually zero. Thus, when starting to take a bend, as a result of there being a simultaneously tiltable directionally controllable wheel, the steering load will be highest initially and then gradually reduce as the tilted position of equilibrium is approached more closely while the vehicle is following the desired bend. It will be clear that by correct dimensioning of the control system the time which elapses between starting to take the bend and achievement of the tilted position of equilibrium can be short, by which means characteristics which correspond to the cornering characteristics of modern motorcycles can be achieved.
A position sensor can be incorporated in the control circuit in order, for example, to make the tilt speed proportional to the movement of the steering wheel. For example, the tilt speed is then lower the greater the inclination with respect to the vertical. Moreover, by this means a change in steering force which is proportional to the movement of the steering wheel can be achieved, so that a greater steering force is demanded for sharper bends. Furthermore, it is then also possible for the tilt speed back to the upright position to be higher the greater the tilt from the upright position.
It is preferable for a small restoring force to be exerted continually in a tilted position of equilibrium, so that a torque or a force can be continually exerted on the steering wheel. When the steering wheel is released, the vehicle will then automatically seek the neutral position for straight line travel. Resetting of this type can be achieved, for example, by correct positioning of linking elements and actuating contacts and short-circuit contacts in connection with, for example, a twistable component, as will be seen more clearly from the description of the appended figure.
Operation of the control system according to the invention can be speed-dependent, so that the system is completely inoperative, for example, when driving into or out of a parking space and/or carrying out other manoeuvres at low speed. Moreover, a power steering system known per se, which is likewise controlled dependent on speed, as is frequently customary, can be incorporated between the steering wheel and the directionally controllable wheel.
In order to execute the tilting movement, especially in the case where one section of the vehicle is hinged with respect to a section of the vehicle which does not change position, it is preferable to make use of one or more sets of drive elements, which assume a limit position when the vehicle is in the neutral (upright) position. The neutral position can be achieved simply in this way and the drive elements require no special adjustment for this purpose. Tilting from the neutral position can then be achieved by actuating one or other of the drive elements. In this context use can be made, for example, of a set of double-acting cylinder/piston assemblies, as is described and shown in more detail in the following description of the figure.
Tilting can also be achieved by, for example, lengthening or shortening the wheel suspension, as described, for example, in GB-A-2 148 217.
The invention is employed for both three-wheeled and multi-wheeled vehicles. In the case of a three-wheeler, two rear wheels arranged some distance apart on either side of the central longitudinal axis and a single front wheel arranged on the central longitudinal axis can be considered. In the case of multi-wheeled vehicles, two front and two rear wheels of the same or virtually the same track width, as for conventional cars, can be considered.
For advantageous functioning of the system even at low drive speeds, it is preferable to allow the drive wheels positioned on or essentially on a common radius of a bend to differ in respect of circumferential speed. In the case of the (rear) wheels driven centrally from a common drive motor, this can be achieved by means of a differential. For particular conditions, a differential action of this type can be temporarily lockable, optionally gradually, for example depending on the drive speed or the magnitude of a prevailing torsion between the drive wheels.
A further aim of the invention is to achieve a tilting effect with a vehicle which has at least two directionally controlled wheels on the same or essentially the same axle and which has an appreciable track width, that is to say a gap between the wheels which is appreciably greater than several times, for example five times, the tire width.